Crystal structure and magnetic properties of the organic antiferromagnet (C(1)TET-TTF)(2)Br

The organic charge transfer complex (C(1)TET-TTF)(2)Br was investigated for its crystal structure, band structure, resistivity, electron spin resonance, and static susceptibility. The crystal structure is characterized by two-dimensional theta-type donor sheets, where the donor arrangement consists of uniform stacking with the absence of dimerized donor molecules. The electrical resistivity shows semiconductive behavior in conflict with the quasi-two-dimensional metallic band structure calculated by the tight binding approximation. These findings show characteristics of the Mott insulating state in this complex. The magnetic susceptibility indicates the feature of an S=1/2 two-dimensional triangular lattice Heisenberg antiferromagnet comprising localized magnetic moments on the donor molecules. It shows an antiferromagnetic transition at T-N=3 K.